Chair back



FIG. 1 is a front side perspective view of a chair back showing my new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a right side elevational view thereof; and

FIG. 5 is a left side elevational view thereof.

FIG. 6 is a top plan view thereof; and,

FIG. 7 is a bottom plan view thereof.

The broken lines shown in FIG. 1 are for illustrative purposes only and form no part of the claimed design. 

The ornamental design for a chair back, as shown and described. 